1. Field of the Invention
The invention relates to telecommunications, and in particular, to emergency call services, provisioning and termination.
2. Description of the Prior Art
Telecommunication service providers are increasingly required to provide location determination services for emergency service calls. For instance, when a wireless caller places a 911 call, the service provider carrying or otherwise handling the call must have the capabilities to determine the physical location of the caller. The public service answering point (PSAP) selected to handle the call can then use the location information to locate, find, and respond to the caller.
Often times, service providers provision their networks regionally. Typically, a single call processing center is assigned to a single region, such as a metropolitan region. Most regions include multiple PSAPs. In most cases, location determination systems exist to assist the call processing center with determining the geographical location of a caller.
A call processing center typically interfaces with location determination systems to initiate location processes and otherwise service emergency calls. An important facet of emergency call provisioning is the selection and distribution of a key that is utilized during a call to correlate information on the call by a wide variety of network elements. The key is typically selected from a finite pool of keys by the location determination system with which the call processing center interfaces. The key selection is then communicated by the call processing center to other elements, such as a PSAP, that need the key for information correlation purposes.
In many regions, the location determination system includes multiple sub-systems. Often times, the sub-systems are redundant. In these cases, the call processing center in a region may still communicate with only one of the sub-systems when provisioning an emergency call. The multiple sub-systems select keys from a shared pool of finite keys. Thus, when a call processing center communicates with one of the sub-systems on an emergency call, the one sub systems selects and reserves a key from the pool of keys. The other sub-system is prohibited from using the same key for any other calls that may be initiated to that other sub-system. An example of a sub-system is a mobile positioning center.
Problematically, when a call terminates, only one of the sub-systems is typically alerted of the termination. The one sub-system then releases the reserved key back to the pool of keys. However, the other sub-systems still holds the key in a reserved state. As a result, the other sub-system has one less key available for new calls. In times of high volume or congestion, such a situation can hinder emergency call processing and response.
FIG. 1 illustrates communication network 100 in an example of the prior art further describing the problems described above. Communication network 100 includes caller 101, communication network 110, call processing system (CPS) 121, public safety answering point (PSAP) 141, PSAP 151, and location provisioning system (LPS) 130. LPS 130 includes sub system 131 and sub system 132. Caller 101 is operatively coupled to communication network 110. CPS 121 is operatively coupled with communication network 110 and LPS 130, and in particular, with sub systems 131 and 132. PSAP 141 and PSAP 151 are also operatively coupled with communication network 110.
FIG. 2 illustrates an operational flow diagram describing the operation of communication network 100 in an example of the prior art. To begin, caller 101 places a 911 emergency services call to CPS 121. CPS 121 generally processes the call or call request to setup and connect the call to one of PSAP 141 or PSAP 151. CPS 121 selects either PSAP 141 or PSAP 151 based on the geographical location of caller 101. In the context of this example, it will be assumed that CPS 121 selects PSAP 141.
Sub system 131 and sub system 132 provide redundant location determination services for emergency calls placed to CPS 121. CPS 121 typically alternates communications between sub system 131 and sub system 132.
Upon receiving the call request, CPS 121 transmits a key request to sub system 131. The key request is typically part of a message sequence exchanged between CPS 121 and sub system 131 to determine the geographical location of caller 101.
Sub systems 131 and 132 store a pool of keys that are assigned to each 911 call initiated by CPS 121. The key is used by CPS 121 and other call elements, such as those elements within PSAP 141, to correlate call information for the emergency services call. After selecting the key, sub system 131 provides the key to CPS 131. The key is thereafter reserved or restricted by both sub system 131 and 132 from any use on any other calls.
CPS 121 responsively initiates call setup to PSAP 141, such as by transmitting call signaling. Included within the call setup process is a transfer of the key to PSAP 141. PSAP 141 queries sub system 131 with the key to obtain location information for caller 101. Sub system 131 initially responds with the location information. PSAP 141 continues a message dialogue with sub system 131 to maintain the location information.
Ultimately, a voice path is established between caller 101 and a termination point within PSAP 141, such as a phone, terminal, or computer of personnel within PSAP 141. The personnel can direct other personal, such as emergency service responders, to the location of caller 101.
Eventually, the call ends and caller 101 terminates the call, such as by hanging up, powering off, or otherwise ending the call. Caller 101 responsively transmits a termination message to CPS 121 alerting CPS 121 that the call has ended. CPS 121 forwards or generates and transmits a termination message to sub system 131. Sub system 131 responsively returns the reserved key to the pool of keys.
Unfortunately, a problem arises whereby sub system 131 is alerted of the call termination by CPS 121, but sub system 132 remains uninformed of the call termination. Thus, while sub system 131 returns the key to the key pool stored internally to sub system 131, sub system 132 maintains the key in a reserved or restricted state. As a result, the total number of keys available for emergency service calls is reduced. In times of high call volume, the pool of keys available to sub system 132 could become severely limited, if not exhausted entirely.